usb: gadget: pch_udc: fix sparse warnings

fix the following sparse warnings:

drivers/usb/gadget/pch_udc.c:1483:9: warning: context imbalance in 'complete_req' - unexpected unlock
drivers/usb/gadget/pch_udc.c:2408:28: warning: context imbalance in 'pch_udc_svc_control_out' - unexpected unlock

Signed-off-by: Felipe Balbi <balbi@ti.com>